Sample processing by tabling for refractory impurities detection and analysis in glass sand.

Refractory minerals, which means mineral grains failing to melt in the glass mix when heated at the usual glass melting temperature, are very noxious impurities, and the glass sands containing even a fraction of ppm of these impurities are rejected by glass makers. Common minerals species, such as corundum, zircon, chromite, the alumino-silicates family, fall within the black list; detection of these impurities, at the level of single grains in 100 kg batches, can be performed only by heavy liquids separation followed by microscopic analysis. In order to reduce the sample to an amount small enough to perform heavy liquid separation, some gravimetric pre-concentration is needed. The authors checked the merits, the difficulties and the still to be solved problems of tabling, when used to this aim, and suggest some way out, on the basis of the results of a test campaign developed on behalf of an important sand marketing firm